One way to study online motor control is to require a modification of the movement during its execution such that the reorganization of some characteristics of the movement highlights the central mechanisms involved in achieving the goal of the movement. It remains, however, to investigate to which extent attentional and motor preparation processes can play a role in the correction of goal-directed movements. Orienting of attention and motor preparation have been generally considered as two different series of processes mostly studied independently from each other. Attentional processes are supposed to facilitate the perceptual and decisional stages of information processing without any regard to the motor components of the task. Similarly, preparatory processes are supposed to facilitate the motor stages of information processing without any regard to the perceptual components of the task.

Regarding the spatial orientation of visual attention, Posner’s work constitutes the most influential model in the field. In the classical paradigm, a central cue is presented at fixation and is supposed to orient the subject’s attention towards a stimulus location. In 80% of the trials, the stimulus is presented in the cued location (valid condition) whereas in the remaining 20% of the trials the stimulus is presented in the uncued location (invalid condition). In an additional condition (neutral condition), the subject’s attention is not cued towards a specific location. The response to the stimuli is given by pressing a single key. It is generally shown that valid RTs are shorter than neutral RTs which are in turn shorter than invalid RTs. The greater efficiency for processing the information to which attention is paid is called an attentional benefit whereas the diminished efficiency for processing the information to which attention is not oriented is called an attentional cost with respect to the neutral condition in which no attention is paid at all.

On the other hand, motor preparation results in a decreasing reaction time as the number of movement features previously known by the subject increases. In the classical experimental paradigms, the conditions of movement initiation were manipulated by modifying the probabilities of performing one movement with respect to others. It has been shown that motor preparation allows to compute in advance, prior to the response signal, one or several motor parameters or to preselect a motor response to the most probable event.

One major problem for motor control is interfacing sensory information and motor programs in a common frame of reference. That is, for example, integrating both visual information about target location and multimodal information about motor commands during visuo-manual reaching movements. Therefore, attentional and preparatory processes could be of particular importance for optimizing the organization and control of goal-directed movements. Few studies, however, have considered the possible relationship or similarities between covert orienting of attention and motor preparation. Those mainly interested in the study of attention hypothesized that motor preparation processes could also be involved in the orienting of attention. Similarly, those mainly involved in the study of motor preparation processes suggested that orienting of attention processes should also be taken into consideration. However, to our knowledge, no specific experiment was designed to clearly investigate this presumed relationship.

The purpose of the present work was to investigate the respective contribution of visual attention and motor preparation and their possible interaction in the control of rapid reaching movements. It was based on the assumption that modulating subjects’ attention and/or motor preparation can modify the efficiency of the control of goal-directed movements. In a first experiment, we manipulated the probability of the direction of target displacement. It was expected that the higher the probability the more efficient was movement correction. In a second experiment, the contribution of attentional processes alone to the control of goal-directed movements was investigated. No movement correction was required and subjects had only to detect a more or less probable target displacement. It was expected that subjects should detect target displacement earlier when increasing the probability of the displacement. In the third experiment, we investigated the contribution of motor preparation processes alone to the correction of goal-directed movements. Movement execution was perturbed without changing target location. This was made possible by introducing a mechanical perturbation of the goal-directed movement. It was expected that subjects should faster correct their movement when better prepared for a presumable correction. Overall, it was hypothesized that both orienting and preparation processes can improve the use of a feedforward-based control of movement correction during execution by facilitating both the preprocessing of target displacement and the anticipated specification of some movement correction components.

The purpose of Experiment 1 was to study effects of orienting of attention and motor preparation processes on motor control performances. The experimental task was to reach a first target. On 25% of the trials, a target displacement occurred on the left or right of the initial target, requiring a movement correction towards this new goal. The probability of the direction of target displacement, that is, of the required movement correction, was manipulated. It was hypothesized that some perceptual and executive processes operating during movement correction are modified as a function of the probability that a movement has to be corrected towards a given target. More specifically, the duration of movement correction should decrease when increasing the probability of the direction of target displacement.

Subjects: Six right-handed subjects (all males), aged 19–24, gave informed consent to participate. All subjects were naive as to the purposes of the experiment.

Apparatus: Fig. 1 illustrates the experimental set-up. It was composed of an adjustable seat and a pointing table equipped with a contactor and six light-emitting diodes (LEDs). The contactor (conductive sheet) was placed just in front of the subject. The release of the contactor allowed recording the beginning of the movement. The first LED, placed in front of the subject and 30 cm distance from the contactor, served as a preparatory signal to ascertain that the initial direction of the gaze and the initial position of the hand onto the contactor were aligned along the sagittal axis of the body. The other five LEDs served as targets and were disposed circularly at 40 cm from the contactor. The central LED was in front of the subject. The other four LEDs were, respectively, oriented at 14 and 28 deg on the left and right of the subjects’ sagittal axis, and were at 10 cm distance from each other. Each target was centred on a 4 cm diameter conductive sheet. This conductive sheet defined the accuracy criterion of the pointing and allowed recording the end of the movement.